The weighted inequality for cross-intersecting pairs with profile-dependent skewness

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Let (A1,B1),…,(Am,Bm)(A_1,B_1),\dots,(A_m,B_m) be pairs of finite non-empty subsets of N\mathbb{N}. Write ai=∣Ai∣a_i=|A_i| and bi=∣Bi∣b_i=|B_i| for 1≤i≤m1\leq i\leq m. Assume that

Ai∩Bi=∅(1≤i≤m),A_i\cap B_i=\emptyset\quad (1\leq i\leq m), Ai∩Bj≠∅(1≤i<j≤m),A_i\cap B_j\ne\emptyset\quad (1\leq i<j\leq m),

and Ai∩Bj≠∅A_i\cap B_j\ne\emptyset whenever ∣Ai∣≠∣Aj∣|A_i|\ne|A_j| or ∣Bi∣≠∣Bj∣|B_i|\ne|B_j|. Weighted cross-intersection conjecture. Then

∑i=1m1(ai+biai)≤1.\sum_{i=1}^m\frac{1}{\binom{a_i+b_i}{a_i}}\leq 1.

This asks whether full cross-intersection for pairs with distinct profiles, together with only the stated ordered condition for pairs of the same profile, still implies the Bollobás-type weighted bound. The surrounding examples show that relaxing the ordering condition can allow weighted sums greater than 11, so the validity of this particular relaxation remains unresolved.

References

Primary source

Alex Scott and Elizabeth Wilmer, “Combinatorics in the exterior algebra and the Bollobás Two Families Theorem”, arXiv:1907.06019 (2020).

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